Evolution and Maintenance of Egg Rejection by Hosts as Adaptation Against Conspecific Brood Parasites: An Individual-Based Model
An individual-based simulation model is constructed to explore evolutionary dynamics of the three adaptive traits: (1) proportion of eggs allocated as conspecific parasitism, (2) rejection ability to reject unlike eggs in own nest, and (3) egg appearance. Simulation analysis suggests that egg rejection can logically evolve due to conspecific brood parasitism and that variability of egg appearance plays a key role to determine the evolutionary trajectory of the three adaptive traits. If variability of egg appearance is small enough, conspecific parasitism selects for lower inter-clutch variation, and all individuals have nearly identical eggs. The population converges to a state where ability to recognize and reject unlike eggs is neutral to selection, and a small cost ignored in this model will suffice to prevent the evolution of egg rejection. However, if egg variability is large enough, conspecific parasitism selects for rejection ability to increase but this in turn selects against conspecific parasitism. The population converges to a state where all individuals show rejection ability at a high level but invest fewer eggs to conspecific parasitism. I highlight the importance of variability of egg appearance for the evolution and the maintenance of egg rejection ability in conspecific brood parasites and call for quantitative measures of the variability of egg appearance in bird species that practice conspecific brood parasitism.
I thank Manolo Soler for giving me a chance to write a chapter for this book. I also thank N. Baran, T. Grim, and M. Soler for constructive comments and suggestions to improve the chapter content.
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